To improve the safety of low-voltage switchgear, various attempts have been made to provide protection against personnel coming into contact with live components. Usually, this has been accomplished by the use of electrically insulating screens, certain of which, at least in switchgear having withdrawable apparatus groups, have to be movable. Thus, stationary insulating screens are often arranged in front of the busbars, said screens having apertures for the connection of electrical coupling devices to, and their disconnection from, the busbars, which apertures are automatically covered by movable screens when an apparatus group is withdrawn from the switchgear cubicle. The provision of movable screens of this kind is complicated and expensive. In addition, the screens usually render it impossible to effect a replacement, under voltage, of one apparatus group by another apparatus group of a different size, since the spacing apart of the connection apertures provided in the screens is not usually suitable for the replacement group.
It is also known previously to use semi-protected busbars in low-voltage switchgear. (By the term "semi-protected busbar" is meant a busbar in which it is not possible to touch a live part of the bar with a standardized test finger positioned in any conceivable manner.) However, the design of these busbars has been such that it has only been possible to carry out connections to the busbar using special screw connection coupling devices.
The present invention aims to provide a combination of a semi-protected busbar and at least one electrical coupling device, in which said at least one coupling device may be of the screw connection type and/or the plug-in type as desired by the user.